There are numerous applications where platform scales are used to obtain the net weight of the load carried by a truck or other motor vehicle. For example, in the buying and selling of bulk grain, the sales or purchase price is usually determined by calculating the net weight of the grain carried by the truck. Similarly, household moving companies usually calculate their moving charges based upon the net weight of the load carried by the moving van.
In these applications, the net weight of the load is determined by weighing the vehicle twice, once when fully loaded to obtain the gross weight of the vehicle, and once when empty to obtain the unloaded weight or tare weight of the vehicle. From these two weights, the net weight of the load may be readily calculated by subtraction.
In this type of weighing operation, the driver of the motor vehicle being weighed may sometimes purposefully or inadvertently position his vehicle for weighing with one or more of the wheels located off of the weighing platform. In such event, the weight registered by the scale would be lighter than the actual weight of the vehicle. If this occurs when the unloaded or tare weight is being determined, the net weight of the load determined from these weighings will be inaccurately high.
A platform scale includes a weighing platform which is flush mounted in the roadbed to facilitate driving the vehicle onto the weighing platform and which is typically about ten feet wide by thirty to sixty feet in length. The scale operator is usually located in a scale house positioned to one side of the weighing platform, and from this vantage point, it is often difficult for the scale operator to ascertain whether the vehicle is properly positioned on the weighing scale. Since the operator's view is obstructed by the motor vehicle, it may be extremely difficult for the scale operator to detect an improperly positioned vehicle. Also, particularly with relatively long tractor trailer vehicles with tandem rear axles, the motor vehicle may be positioned on the scale with one or more of the rearmost axles located off of the weighing platform. It is difficult for the scale operator to detect this from his vantage point in the scale house. Even if the scale operator has a clear vantage point of all portions of the weighing platform, the routine nature of the weighing operation may frequently give rise to carelessness on the part of the scale operator whereby improperly positioned vehicles may go undetected during weighing.
From the foregoing, it should be apparent that the need exists for a device and method for insuring that a motor vehicle is properly positioned on the weighing platform of a platform scale prior to weighing, and it is an important object of the present invention to provide a device and method for satisfying this need.
It is a further object of this invention to provide a device and method of the type described which may be readily installed and used on existing platform scales without requiring substantial modification thereto.